Condensation of halohydrocarbons

ABSTRACT

A process for condensing halogenated hydrocarbon which comprises bringing a stream comprising halogenated hydrocarbon vapour, water vapour and non-condensable gases into direct contact with a liquid medium which is maintained at a subnormal temperature sufficient to condense both the halogenated hydrocarbon vapour and the water vapour and which retains condensed water in the liquid phase.

United States Patent [1 1 Morris Aug. 21, 1973 CONDENSATION 0F 3,400,512 9/1968 McKay 55/82 HALOHYDROCARBONS 2,765,049 10/1956 Nafziger 55/29 3,403,522 10/1968 Henry 55/31 [75] lnventor: Victor William Morris, Runcorn,

England [73] Assignee: Imperial Chemical Industries Primary Examiner-Charles t Limited, London, En land Attorney-Cushman, Darby & Cushman [22] Filed: Nov. 12, 1970 [21] Appl. No.: 88,649

[57] ABSTRACT [30] Foreign Application Priority Data Dec. 5, 1969 Great Britain 59,511/69 A Process for condensing halogenated hydrocarbon which comprises bringing a stream comprising haloge- 52 us. Cl. 55/29 mated hydrocarbon vapour, water vapour and [51] Int. Cl. B0ld 53/16 n nsa gas s int direct Contact with a liquid me- [58] Field of Search 55/29-32, 82 dium which is maintained at a Subnormal temperature 5 sufficient to condense both the halogenated hydrocarbon vapour and the water vapour and which retains [56] References Ci d condensed water in the liquid. phase.

UNITED STATES PATENTS 3,589,104 6/1971 Panzanella 55/32 2 Claims, 1 Drawing Figure PATENTEDAUGZIW- I 3753335 I nvenlor V/erae M4 1 //7M No 02/5 A ttorneys CONDENSATION OF HALOHYDROCARBONS This invention relates to an improved process for the condensation of halogenated hydrocarbons.

Streams comprising halogenated hydrocarbon vapour, water vapour and non-condensable gases are encountered in industry and difficulties arise in the condensation of the halogenated hydrocarbon vapour. It is a common enough procedure to recover halogenated hydrocarbons from such a stream by bringing the stream into indirect contact with a fluid maintained at sub-zero temperatures (below C) circulating in a condenser. The halogenated hydrocarbon is thereby condensed and other components of the stream, for example, nitrogen pass out of the system as uncondensed gases. However, as the stream contains water vapour, ice is deposited on the condenser surface and this seriously affects heat exchange between the stream and the cold fluid. Furthermore ice can block the plant, for example in pipelines and in valves. The problem can be so acute that it becomes necessary to duplicate the condensation system so that while one system is in operation the other is being freed from ice.

It is an object of the present invention to provide an improved process which enables halogenated hydrocarbons to be condensed while at the same time it also avoids formation of ice.

According to the present invention therefore we provide a condensation process which comprises bringing a stream comprising halogenated hydrocarbon vapour, water vapour and non-condensable gases into direct contact with a liquid medium which is maintained at a sub-normal temperature sufficient to condense both the halogenated hydrocarbon vapour and the water vapour and which retains condensed water in the liquid pha e.

The liquid medium should be inert to the halogenated hydrocarbon. Good results are obtained when there is employed as liquid medium an aqueous solution of a metal salt which is substantially immiscible with the condensed halogenated hydrocarbon. Good results are obtained when using an aqueous calcium chloride brine. The concentration of calcium chloride brine will be such that freezing out or crystallisation of a solid phase does not occur at the lowest temperature employed in the system.

The present process is applicable to the treatment of a single halogenated hydrocarbon or mixtures thereof and finds its widest application in the treatment of chlo-. rinated hydrocarbons. The water vapour associated with the halohydrocarbon may have been picked up by treatment of a hot crude exit stream. from a'reactor with aqueous quenching and washing treatments. For example in the oxychlorination of ethylene the crude exit product may be submitted to various aqueous quenching and washing steps to reduce the temperature of the stream, to condense some of the 1,2- dichloroethane and to remove hydrogen chloride contained in the stream. Such a stream containing l,2-. dichloro-ethane vapour, water vapour and large amounts of uncondensable gases such as unreacted ethylene and nitrogen are eminently useful for treating according to the process of the present invention. The temperature of the calcium chloride brine is suitably in the range 0C to 40C and of concentration to 32 percent by weight calcium chloride, when treating a stream comprising l,2-dichloroethane vapour, water vapour and non-condensable gases which is at a temperature in the range 50 to 0C.

Direct contact of the stream with the liquid medium can be easily effected, for example, in ring-packed towers or in trayed columns. The condensed halogenated hydrocarbon and liquid medium, for example, calcium chloride brine, are separated and the condensed halohydrocarbon, e.g. 1,2-dichloroethane is recovered. Conventional means may be provided for purifying the condensed halohydrocarbon, e.g. by fractional distillation. Water entrapped from the stream by the liquid medium, e.g. calcium chloride brine, can be removed by purging part of the brine or by concentrating the brine.

One suitable type of apparatus for carrying out the process of the invention is described in the accompanying drawing which is not drawn to scale. In the drawing 1 is a ring-packed tower, 2 is an inlet for the stream comprising halogenated hydrocarbon vapour, water vapour and non-condensable gases. 3 is an inlet for cold calcium chloride brine. 4 is a pipe for removing a mixture of calcium chloride brine and condensed halogenated hydrocarbon. 5 is a gravity separator. 6 is a pipe for withdrawal of the condensed halohydrocarbon layer. 7 is a pipe for withdrawal of calcium chloride brine which passes via pump 8, pipes 9 and 10, and cooler 11 to pipe 3. 12 is a pipe for withdrawal of a small amount of calcium chloride brine. 13 is a pipe for discharge of uncondensed gases and vapours.

Reference is now made to one particular process according to the invention carried out under specific conditions when using the apparatus illustrated in the drawing. A stream (3250 kg/hr) at a temperature of 5C and at a pressure of 5 ats gauge consisting of kg/hr 1,2-dichloroethane vapour, 5 kg/hr water vapour, the remainder being nitrogen, carbon dioxide and ethylene is passed through pipe 2 to the tower 1. The latter is 30 ft high and 2 ft diameter and is packed with 1% inch Raschig rings. The stream meets a flow of 5% m /hr of calcium chloride brine of concentration 25 to 32 percent by weight calcium chloride which is at a temperature of 30C and enters via pipe 3 and flows down tower 1. A mixture of condensed 1,2-dichloroethane and calcium chloride brine at 22C leaves the tower via pipe 4 to settle in gravity separator 5. A bottom layer of condensed 1,2-dichloroethane leaves the separator via pipe 6. Calcium chloride brine leaves the separator via pipe 7 and passes via pump 8 and pipes 9 and 10 to cooler 11 (through which is passed a refrigerant) and so to pipe 3 and tower 1. Nitrogen, carbon dioxide, ethylene and a little l,2-dichloroethane vapour leave the tower via pipe 13 at 28C. A small amount of calcium chloride brine leaves via pipe 12 for purging of part of the aqueous phase.

Although the process has been particularly described with reference to use of calcium chloride brine other liquid media can be used. Thus organic liquids, for example, ethylene glycol, may be employed. If the organic medium is miscible with the condensed halohydrocarbon then the condensed water will be associated with the medium in the mixed phase. Under such conditions the mixed phase can then be submitted to fractional distillation to separate the various components of the phase.

What we claim is:

l. A condensation process which comprises bringing a stream comprising 1,2-dichloroethane, water vapor dichloroethane.

2. A process as claimed in claim 1, in which the stream comprises 1,2-dichloroethane vapour, water vapour and non-condensable gases including ethylene and nitrogen produced by the oxychlorination of ethylene followed by aqueous quenching and washing steps. 1' 8i i i 

2. A process as claimed in claim 1, in which the stream comprises 1,2-dichloroethane vapour, water vapour and non-condensable gases including ethylene and nitrogen produced by the oxychlorination of ethylene followed by aqueous quenching and washing steps. 